DESCRIPTION (adapted from the Abstract): Progressive multifocal leukoencephalopathy (PML) is a fatal, immunodeficiency-associated demyelinating brain disease that results from selective, lytic infection of oligodendrocytes by a 5.1 kb DNA virus, JC virus. PML is no longer a rare condition, as it is now diagnosed in 5% of patients with AIDS. Although JC virus oligodendrocyte specificity is known to arise from glial-specific transcriptional regulation of viral early gene expression, the molecular mechanism of this regulation remains unclear. Study of JC virus biology is important because new therapies for this currently untreatable infection are most likely to result from scientific advances. JC virus early promoters have been cloned directly from human brain. By using a deletion/mutation approach to functional analysis, these researchers found that glial-specificity is directed by the basal promoter region, instead of the stream enhancer-like tandem repeats. Furthermore, they showed that the viral protein, large T-antigen regulates the basal promoter in a cell-specific manner, strongly activating expression in nonglial cells, but repressing expression in glial cells. This cell-specific regulation is dependent upon the JC virus TATA box. These findings strongly suggest that the basal region of the JC virus early promoter is selectively repressed in nonglial cells. Because preliminary data suggest that the JC virus early promoter in nonglial cells, the Investigator hypothesizes that a repressor protein is required to block default expression of the promoter in nonglial cells. The goal of the proposed research is to test this hypothesis by identification of the putative repressor. In Aim #1 the Investigator and associates will seek to identify DNA sequences in the basal promoter region that mediate cell-specificity. In Aim #2 they will examine cell-specific regulation of the JC virus early promoter by large T-antigen, in anticipation that differential regulation of the JC virus promoter by T-antigen is related to the mechanism of cell specificity and, thus, offers a window into understanding the promoter. In Aim #3 they will employ a candidate protein approach to the identification of the putative repressor, using the transcriptional repressors p53 and Dr1.